The mentioned adsorption cycles are used in PSA installations which comprise a large number of valves having a high frequency of opening/closing.
Given that the good operation of the cycle depends on the sequences of opening and closing these valves, which permit obtaining the foreseen pressure cycle, it will be easily seen that the malfunction of one of these valves which are manipulated at each cycle, can cause serious problems in the operation of a PSA installation.
By way of example, there can be distinguished in particular two cases of malfunction relating to these valves:
1) A first malfunction can consist of mechanical blockage of the valve, resulting in that either the valve remains closed despite receiving an opening signal (or conversely), or it opens or closes only very slowly.
Such incidence can be detected by end of path detector installed at the level of the veins and if desired connected to timers.
Moreover, given that this type of malfunction generally causes substantial unbalance in the pressure cycle of the various adsorbers, such an incident is relatively easy to identify.
2) A second malfunction can result from a defect of sealing of a closed valve, which leads to internal loss either between adsorbers or between one adsorber and the production line or the residual line.
In contrast to mechanical blockage, unsealed closed valve losses are difficult to detect in an operating unit.
They nevertheless translate to decreased performance of the PSA installation due either to unbalanced operation of the adsorbers, or directly a production loss in the residual gas line.
To detect valves having in their closed position a sealing fault, there are conventionally used periodic stoppages of the operation of the installation to carry out tests of sealing.
But these controls have the drawback that they are long and intricate. Moreover, given the duration of stoppage of the installation, these controls can only be carried out at spaced time intervals.
However, given that the loss of production caused by a sealing defect of a valve and translating into a loss of several percent of the extraction output can last several months, the loss can be very great.